Recently, in the research field of biology, observations have been made with specimens excised, for example, from the brain. To make the observations be representative of living tissue to the maximum extent possible, it is desirable to observe inside the specimen in areas which have less damage from cutting. To do so, it is necessary to prepare the specimen with as little damage as possible. Therefore, there has been a recent trend to increase the thickness of the specimen. It is common to make observations using infrared light with wavelengths ranging from 700 nm to 1200 nm. These wavelengths provide good permeability with less scattering in order to observe areas inside the thick specimens, as published in Japanese Patent Publication H10-20198.
Also, in the field of observing biological samples with a microscope, what is termed a xe2x80x9cpatch clampxe2x80x9d method is widely used. In this method, a micro-electrode made of glass having a diameter of only a few microns is glued to the surface of a cell membrane using a manipulator. This allows, for example, the electric properties of the calcium channel of the cell membrane to be investigated.
After searching to locate the specimen using a low magnification objective lens of a microscope, it is then necessary to switch the degree of the magnification in order to enlarge the viewed image. This allows cells of the specimen to be observed with high magnification and allows one to conduct operations as described above, as well as to observe the cells using fluorescence.
In the prior art, switching the degree of magnification in a microscope is conducted by arranging both a low magnification objective lens and a high magnification objective lens on the revolver of a microscope. Rotation of the revolver inserts and withdraws the low magnification objective lens and the high magnification objective lens, in an alternating sequence, into the light path. However, there is quite a mechanical shock to the system upon switching objective lenses by operating the revolver, and therefore it is difficult to keep the specimen from being disturbed during this process. In particular, in the case of the xe2x80x9cpatch clampxe2x80x9d method, contact of the objective lens with one or more tools needed in performing the method, such as the micro-electrode, is likely to occur. As a result of either actual contact or mere vibration during the changing of objective lenses in order to change magnification, the micro-electrode""s needle-shaped tip sometimes slips out of the specimen or the specimen moves out of the field of view. This requires that the same operation as before be performed again, after first switching back to the low magnification objective lens in order to locate the specimen once more. As can be imagined, this results in decreased efficiency.
In situations in which observations are also to be made using a different range of wavelengths, an operation such as switching one or more filters in the illuminating or transmitted light paths, or switching the light source itself, becomes necessary. There is quite a mechanical shock to the system upon switching these items as well. Thus, such switching operations can also cause the micro-electrode""s needle-shaped tip to slip out of the specimen or the specimen itself to move relative to the field of view.
The object of the present invention is to enable a microscope user to be able to switch from a relatively wide field of view having a low magnification to a relatively narrow field of view having high magnification without having to rotate a different object lens into the light path, and to enable observations to be made using different wavelength ranges without requiring a switching operation of filters or light sources that causes mechanical shock to the specimen being viewed.